For replacement of the ankle joint, an endoprosthesis is known which consists of a component to be connected to the anklebone, a component to be connected to the tibia, and a middle part (DE-U-8812806; brochure entitled “LINK S.T.A.R. Totale Sprunggelenkprothese [H. Kofoed] by the company Waldemar Link (flexion and extension in the sagittal plane. The tibial component and the middle part form interacting slide surfaces which permit a rotation about the vertical axis. They can be made flat in order to GmbH & Co.), Hamburg). The anklebone component and the middle part interact via slide surfaces which permit compensating movements in the AP (anterior-posterior) direction and LM (lateral-medial) direction. Stabilization is effected by means of the natural ligament apparatus.
In the known prosthesis, the upper and lower slide surfaces of the middle part are oriented parallel to one another in the frontal plane. This is logical insofar as the aim is to replace the natural slide surfaces of the anklebone and of the tibia with the prosthetic slide surfaces, without any associated change in direction. However, it has been found that, after surgery, the collateral and medial ligaments of the ankle often have different tensioning, which can cause difficulties.